GB2358044A

GB2358044A - Hydraulic circuit having pressure equalization during regeneration

Info

Publication number: GB2358044A
Application number: GB0029192A
Authority: GB
Inventors: Hearn Michael A A; Sr Thomas J Hajek; Larry W Lorimor; Daniel T Mather; Tolappa T Srikrishnan
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 1999-12-15
Filing date: 2000-11-30
Publication date: 2001-07-11
Anticipated expiration: 2020-11-30
Also published as: GB0029192D0; JP4707827B2; JP2001208008A; DE10058979A1; DE10058979B4; US6955115B1; GB2358044B

Abstract

A fluid system (10) is provided wherein two different fluid circuits (12 and 14) are connected in parallel with a single source of pressurized fluid (16) and the two fluid circuits can function together even when one of the loads is lighter than the other. This is accomplished by having the lightly loaded circuit (12) having a directional control (24) that when operated in one of its operative positions the flow from the rod end (30) of the cylinder (26) is directed through the directional control valve (24) and combined with the supply flow being directed to the head end (28) of the cylinder (26). With the other heavier loaded circuit (14) also being actuated, the pressure of the fluid from the rod end (30) of the fluid cylinder (26) is equalized with the pressure of the heavier loaded circuit (14). Consequently, the speed of the heavier loaded circuit (14) does not stall or slow down relative to the lightly loaded circuit (12). In the case of a machine having a bucket used for backdragging, the circuit needs a diverter system that provides protection from the cylinder rod of the fluid cylinder (26) from buckling during backdragging while maintaining the ability for pressure equalization when not performing a backdragging operation.

Description

2358044 1 1 HYDRAULIC CIRCUIT HAVING PRESSURE 2 EQUALIZATION DURING

REGENERATION 3 4

6 Technical Field

7 This invention relates generally to a fluid 8 system having at least two different fluid circuits 9 being supplied in parallel by only one fluid source and more particularly to fluid system wherein the two 11 parallel fluid circuits having different loads may be 12 operated simultaneously and wherein undue back 13 pressure can be overcome when performing predefined 14 work functions.

16 Background Art

17 It is well known that when operating two 18 different fluid circuits in parallel with a common 19 pump, the circuit having the lightest load will automatically take the pump's flow. Likewise, the 2 1 circuit with the heaviest load will stall or slow to 2 such an extent that the operation of that circuit is 3 severally hampered. It is also desirable in many 4 systems with a light load to recombine the flow from one end of a cylinder to the other end. However, 6 this has proved to be difficult since it required 7 special valving in the main control spool or added 8 valving. Even then, the functioning of the heavy 9 loaded circuit would either slow or stall. In attempts to overcome the stalling of the heavy loaded 11 circuit, excessive pressures would be generated in 12 the fluid system. Some systems would provide 13 regeneration of exhaust fluid to the other end of the 14 cylinder by placing a restriction in the exhaust line and forcing the fluid to recombine with the flow from 16 the pump as the flow entered the main control valve.

17 When operating two separate circuits in parallel, 18 this type of recombining does not work since the 19 circuit with the heavier load would still stall or slow because the pump's flow would go to the circuit 21 with the lightest load.

22 The present invention is directed to 23 overcoming one or more of the problems as set forth 24 above.

26 Disclosure of the Invention

27 According to a first aspect of the present 28 invention there is provided a fluid system in

Claims

29 accordance with Claim 1.

In one aspect of the present invention, a 31 fluid system is provided and includes a single source 3 1 of pressurized supply fluid that receives fluid from 2 a reservoir and is operable to control multiple 3 loads. The fluid system further includes first and 4 second fluid circuits connected in parallel to the single source of pressurized supply fluid. The first 6 fluid circuit is connected to the single source of 7 pressurized supply fluid and has a first directional 8 control valve connected to a first fluid cylinder.

9 The first fluid cylinder has head end and rod end ports. The first directional control valve has a 11 supply inlet port connected to the single source of 12 pressurized fluid, first and second outlet ports 13 connected to the respective head end and rod end 14 ports of the fluid cylinder, and an exhaust port is connected to the reservoir. The first directional 16 control valve is movable between a center position 17 and first and second operable positions. In the 18 center position, the supply port, the first and 19 second outlet ports and the exhaust port are blocked from one another. In the first operable position, 21 the supply port is in communication with the second 22 outlet port and the first outlet port is in 23 communication with the exhaust port. In the second 24 operable position the supply port is in communication with the first outlet port and the second outlet port 26 is in communication with the supply port. The second 27 fluid circuit is connected to the single source of 28 pressurized supply fluid in parallel with the first 29 fluid circuit and has a second directional control valve connected to a second fluid cylinder. The 31 second fluid cylinder also has head end and rod end 4 1 ports. The second directional control valve has a 2 supply inlet port connected to the single source of 3 pressurized fluid, first and second outlet ports 4 connected to the respective head end and rod end ports of the second fluid cylinder, and an exhaust 6 port connected to the reservoir. The directional 7 control valve is movable between a center position 8 and first and second operable positions. In the 9 center position the supply port is blocked from the first and second outlet ports and the head end and 11 rod end ports are blocked from the exhaust port. In 12 the first operable position the supply port is in 13 communication with the second outlet port and the 14 first outlet port is in communication with the is exhaust port. In the second operable position the 16 supply port is in communication with the first outlet 17 port and the second outlet port is in communication 18 with the exhaust port.

19 Brief Description of the Drawings 21 Fig. 1 is a schematic representation of a 22 fluid system having two circuits operating in 23 parallel with a single source of pressurized fluid 24 and incorporating the subject invention; Fig. 2 is a schematic representation of the 26 fluid system incorporating another aspect of the 27 subject invention.

28 Fig. 3 is a schematic representation of the 29 fluid system incorporating yet another aspect of the subject invention; and 1 Fig. 4 is a schematic representation of the 2 fluid system incorporating still another aspect of 3 the subject invention.

4 Best Mode for Carrying Out the Invention 6 Referring to Fig. 1 of the drawings, a 7 fluid system 10 is provided and includes first and 8 second fluid circuits 12,14 connected in parallel to 9 a single source of pressurized supply fluid 16 via a supply conduit 17. The source of pressurized supply 11 fluid 16 receives fluid from a reservoir 18. The 12 fluid system 10 also includes a pilot control system 13 20 connected to a source of pressurized pilot fluid 14 22.

is The first fluid circuit 12 includes a first 16 directional control valve 24, a first fluid cylinder 17 26 having a head end port 28 and a rod end port 30, 18 and first and second vented load check valves 32,34.

19 The first directional control valve 24 has a supply port 36 connected to the supply conduit 17, first and 21 second outlet ports 38,40 and an exhaust port 42 22 connected to the reservoir 18. A conduit 44 connects 23 the first outlet port 38 to the head end port 28 of 24 the first fluid cylinder 26 and a conduit 46 connects the second outlet port 40 to the rod end port 30 26 thereof.

27 The first directional control valve 24 is 28 movable between a center position and first and 29 second operable positions. In the center position, the supply port 36, the first and second outlet ports 31 38,40, and the exhaust port 42 are blocked from one 6 1 another. In the first operable position, the supply 2 port 36 is in communication with the second outlet 3 port 40 and the first outlet port 38 is in 4 communication with the exhaust port 42. In the second operable position, the supply port 36 is in 6 communication with the first outlet port 38 and the 7 second outlet port 40 is in communication with the 8 supply port 36. Consequently, in the second operable 9 position of the first directional control valve 24, the supply port is in communication with both the 11 first and second outlet ports 38,40.

12 The first directional control valve 24 is 13 biased to its center position in a conventional 14 manner and is moved to its first and second operable is positions in response to receipt of pressurized pilot 16 fluid from the pilot control system 20 through 17 respective first and second pilot conduits 48,50. A 18 control input arrangement 52 is provided in the pilot 19 control system 20 and includes a first operator controlled input arrangement 54 disposed between the 21 source of pressurized pilot fluid 22 and the first 22 and second pilot conduits 48,50. The first operator 23 controlled input arrangement 54 is operative to 24 control the position of the direction control valve 24 in response to an input by the operator.

26 The first vented load check valve 32 is 27 disposed in the conduit 44 and the second vented load 28 check valve 34 is disposed in the conduit 46. Each 29 of the first and second vented load check valves 32,34 is operative to permit flow to the first fluid 31 cylinder and selectively block flow therefrom. Each 7 1 of the f irst and second vented load check valves 2 32,34 has a pressure chamber 56 defined therein 3 behind the valving element 59. The pressure chamber 4 56 of the first and second vented load check valves 32,34 is connected to the respective head end 28 and 6 rod end 30 of the first fluid cylinder 26 through 7 orificed conduits 58.

8 First and second two-position valves 60,62 9 are disposed between the respective pressure chambers 56 and the reservoir 18. Each of f irst and second 11 two-position valves 60,62 is spring biased to a flow 12 blocking position and movable to a flow passing 13 position in response to receipt of pressurized fluid 14 through respective conduits 64,66 that are respectively connected to pilot conduits 48,50.

16 A diverter valve 68 is disposed in a 17 conduit 69 between head end port 28 of the first 18 fluid cylinder 26 and the reservoir 18 and a relief 19 valve 70 is disposed between the diverter valve 68 and the reservoir 18. The diverter valve 68 is 21 biased to a closed position by a mechanical biasing 22 mechanism 72 and the pressure in the rod end port 30 23 directed thereto through a pilot conduit 74. The 24 diverter valve 68 is urged towards its flow passing position in response to the pressure in the head end 26 port 28 as directed thereto through pilot conduit 76.

27 The second fluid circuit 14 includes a 28 second directional control valve 78, a second fluid 29 cylinder 80 having a head end port 82 and a rod end port 84, and third and fourth vented load check 31 valves 86,88. The second directional control valve 8 1 78 has a supply port 90 connected to the supply 2 conduit 17, first and second outlet ports 92,94 and 3 an exhaust port 96 connected to the reservoir 18. A 4 conduit 98 connects the first outlet port 92 to the head end port 82 of the second fluid cylinder 80 and 6 a conduit 100 connects the second outlet port 94 to 7 the rod end port 84 thereof. A fluid make-up port 8 102 is in continuous communication with the exhaust 9 port 96 in all positions of the directional control valve 78 and a one-way check valve 104 provides fluid 11 communication of the fluid in the exhaust port 96 12 with the supply port 90 and blocks return flow.

13 The second directional control valve 78 is 14 movable between a center position and first and is second operable positions. In the center position, 16 the supply port 90 is blocked from the first and 17 second outlet ports 92,94 and the head end port and 18 rod end port 82,84 of the second fluid cylinder 80 19 are blocked from the reservoir 18. In the first operable position the supply port 90 is in 21 communication with the second outlet port 94 and the 22 first outlet port 92 is in communication with the 23 exhaust port 96. In the second operable position the 24 supply 90 is in communication with the first outlet port 92 and the second outlet port is in 26 communication with the exhaust port 96.

27 The second directional control valve 78 is 28 biased to its center position in a conventional 29 manner and is moved to its first and second operable positions in response to receipt of pressurized pilot 31 fluid from the pilot control system 20 through 9 1 respective third and fourth pilot conduits 106,108.

2 The control input arrangement 52 further includes a 3 second operator controlled input arrangement 110 4 disposed between the source of pressurized pilot fluid 22 and the first and second pilot conduits 6 106,108. The second operator controlled input 7 arrangement 110 is operative to control the position 8 of the second direction control valve 78 in response 9 to an input by the operator.

The third vented load check valve 86 is 11 disposed in the conduit 98 and the fourth vented load 12 check valve 88 is disposed in the conduit 100. Each 13 of the third and fourth vented load check valves 14 86,88 is operative to permit flow to the second fluid is cylinder and selectively block flow therefrom. Each 16 of the third and fourth vented load check valves 17 86,88 also has a pressure chamber 112 defined therein 18 behind the valving element 114. The pressure chamber 19 112 of the third and fourth vented load check valves 86,88 is connected to the respective head end 82 and 21 rod end 84 of the second fluid cylinder 80 through 22 orificed conduits 116.

23 Third and fourth two-position valves 24 118,120 are disposed between the respective pressure chambers 112 and the reservoir 18. Each of third and 26 fourth two-position valves 118,120 is spring biased 27 to a f low blocking position and movable to a flow 28 passing position in response to receipt of 29 pressurized fluid through respective pilot conduits 121,122 that are respectively connected to pilot 31 conduits 106,108.

1 A conventional make-up valve 123 is 2 disposed in a conduit 124 connected between the rod 3 end port 30 of the first fluid cylinder 26 and the 4 reservoir 18.

Referring to Fig. 2 another embodiment of 6 the fluid system is disclosed. Like elements have 7 like element numbers. In Fig. 2, the flow from the 8 pressure chamber 56 is directed from the second two 9 position valve 62 to a connection point 125 between the second vented load check valve 34 and the first 11 directional control valve 24 through a conduit 126.

12 A one way check valve 128 is disposed in the conduit 13 126 and is operative to permit fluid flow from the 14 second vented load check valve 62 to the connection point 125 and prohibit reverse flow therethrough.

16 A two-position bypass valve 130 is disposed 17 in a conduit 132 and connected in parallel with the 18 one way check valve 128 between the second vented 19 load check valve 62 and the connection point 125.

The two-position bypass valve 130 is spring biased to 21 a flow passing position and movable to a flow 22 blocking position in response to pressurized fluid in 23 the fourth pilot conduit 108 connected to the second 24 directional control valve 78 being delivered thereto through a pilot conduit 134.

26 A second diverter valve 136 is operatively 27 disposed in a conduit 137 between the rod end port 30 28 of the first fluid cylinder 26 and the reservoir 18.

29 The second diverter valve 136 is biased to a flow blocking position by a second mechanical biasing 31 mechanism 138 and the pressure in the rod end 30 of 11 1 the first fluid cylinder 26 directed thereto through 2 a conduit 140 and movable towards a flow passing 3 position in response to the pressure of the fluid in 4 the head end 28 of the first fluid cylinder 26 directed thereto through a conduit 142.

6 Referring to Fig. 3, another 7 embodiment of the subject invention is disclosed.

8 Like elements have like element numbers. Fig. 3 is 9 quite similar to Fig. 2. The main differences being that the second diverter valve 136 is not required 11 and the first diverter valve 68 has been modified.

12 The first diverter valve 68 of Fig. 3 is a two 13 position four-way valve connected to the head end 14 port 28 by the conduit 69 and to the rod end port 30 is of the first fluid cylinder 26 through a conduit 144.

16 The four-way diverter valve 68 has a head end exhaust 17 port 146 which directs fluid from the diverter valve 18 68 to the reservoir 18 across the relief valve 70 and 19 a rod end exhaust port 148 which directs fluid from the four-way.diverter valve 68 to the reservoir 18 21 through a portion of the conduit 144. The four-way 22 diverter valve 68 is biased to a flow blocking 23 position by the mechanical biasing mechanism 72 and 24 the pressure in the rod end 30 of the first fluid cylinder 26 directed thereto through the conduits 26 74,144 and movable towards a flow passing position by 27 the pressure in the head end 28 of the first fluid 28 cylinder 26 directed thereto through the conduits 29 76,69.

A two-position blocker valve 150 is 31 disposed in the conduit 144 between the four-way 12 1 diverter valve 68 and the reservoir 18. The two 2 position blocker valve 150 is spring biased to a flow 3 passing position and movable to a flow blocking 4 position in response to pressurized fluid in the fourth pilot conduit 108 connected to the second 6 directional control valve 78 being directed thereto 7 through the pilot conduit 134. The flow blocking 8 position of the two-position blocker valve 150 blocks 9 flow from the diverter valve 68 to the reservoir 18 but permits makeup flow from the reservoir 18 to the 11 rod end 30 of the first fluid cylinder 26.

12 Referring to Fig. 4 another embodiment of 13 the subject invention is disclosed. Like elements 14 have like element numbers. Fig. 4 is similar to Fig.

is 2 except the two-position bypass valve 130 and the 16 second diverter valve 136 are not needed.

17 Additionally, the first diverter valve 68 is a five 18 way, two-position valve and is operatively disposed 19 in the conduit 46 between the rod end port 30 of the first fluid cylinder 26 and the second vented load 21 check valve 34 and operatively connected to the head 22 end port 28 of the first fluid cylinder 26 through 23 the conduit 69. The five-way diverter valve 68 is 24 biased to a first position by the mechanical biasing mechanism 72 and the pressure in the rod end 30 of 26 the first fluid cylinder 26 as directed thereto 27 through the conduit 74 and movable towards a second 28 position in response to the pressure of the fluid in 29 the head end 28 of the first fluid cylinder 26. At the first position of the five-way diverter valve 68, 31 fluid is free to flow between the rod end port 30 and 13 1 the second vented load check valve 34 and flow 2 thereacross through the conduit 9 from the head end 3 port 28 across the relief valve 70 to the reservoir 4 18 and a connection between the rod end port 30 and the reservoir 18 through a conduit 156 are blocked.

6 At the second position of the five-position diverter 7 valve 68, flow from the second vented load check 8 valve to the rod end port 30 is blocked, flow through 9 the conduit 69 is open, and flow between the rod end port 30 and the conduit 156 is open.

11 The two-position blocker valve 150 is 12 disposed in the conduit 156. As previously described 13 with respect to Fig. 3, the two-position blocker 14 valve 150 is spring biased to a flow passing position is and movable to a blocking position in response to 16 pressure of the fluid in the fourth pilot conduit 17 connected to the second directional control valve as 18 directed thereto through the conduit 134. In the 19 blocking position, flow from the two-position, five way diverter valve to the reservoir 18 is blocked but 21 flow from the reservoir 18 to the two-position, five 22 way diverter valve is permitted.

23 It is recognized that various components 24 and/or arrangement could be used in the subject fluid system 10 without departing from the essence of the 26 subject invention. For example, the control input 27 arrangement 52 could be an electro-hydraulic control.

28 Likewise, the first, second, third, and fourth two 29 position valves 60,62,118,120 could be controlled electronically. In the second fluid circuit 14, the 31 two vented load check valves 86,88 could be 14 1 eliminated and the first and second outlet ports 2 92,94 would be blocked from the exhaust port 96 3 instead of being in communication as shown in the 4 drawing. Likewise, even though the single source of pressurized supply fluid 16 is illustrated as a fixed 6 displacement pump, it is recognized that it could be 7 a variable displacement pump and also could be 8 controlled by a load sensing arrangement (not shown) 9 Additionally, the line connecting the respective first, second, third, and fourth two-position valves 11 60,62,118,120 to the reservoir 18 could alternatively 12 be connected to the line downstream of the respective 13 first, second, third, and fourth vented load check 14 valves 32,34,86,88. That is between the respective is load check valves and the directional control valves.

16 It may also be necessary in some instances to connect 17 a check valve in one or more of the lines to inhibit 18 back flow towards the two-position valve. Even 19 though conventional make-up valves are only shown between the rod end port 30 of the first fluid 21 cylinder 26 and the reservoir 18, it is recognized 22 that conventional make-up valves could be provided 23 between the head and/or rod end ports 28,30,82,84 of 24 each of the first and second cylinders 26,80 and the reservoir 18 to ensure that each of the head and rod 26 ends remain full of fluid at all times.

27 28 Industrial Applicabilit 29 In the operation of the subject fluid system 10 of Fig. 1, for example, the first fluid 31 circuit 12 normally has a lighter load than the is 1 second fluid circuit 14. This is typical in 2 machines, such as loaders, wherein the first fluid 3 circuit 12 is a circuit for dumping a bucket and the 4 second fluid circuit 14 is a circuit for lifting the bucket.

6 If the operator desires to lift the bucket, 7 he makes the desired input through the second 8 operator controlled input arrangement 110. A pilot 9 signal is directed through the pilot conduit 108 to move the directional control valve 78 towards its 11 second operable position. This permits the 12 pressurized flow in the supply conduit 90 from the 13 pump 16 to pass therethrough to the head end 82 of 14 the second cylinder 80 to extend the second fluid is cylinder thus raising the bucket. The pressurized 16 fluid acting on the valving element 114 of the third 17 vented load check valve 86 moves it to a flow passing 18 position in a conventional manner.

19 The exhaust flow from the rod end 84 returns to the reservoir 18 through the conduit 100, 21 across the fourth vented load check valve 88 and 22 through the second outlet port 94 and the exhaust 23 port 96 of the directional control valve 78. Since 24 the pilot signal in the pilot conduit 108 is also directed to the fourth two-position valve 120 moving 26 it to its flow passing position, the pressure chamber 27 112 of the fourth vented load check valve 88 is open 28 to the reservoir 18 thus permitting the valving 29 element 114 to lift up in a conventional manner to pass flow therethrough.

16 1 If it is desired to lower the load, i.e.

2 retract the second fluid cylinder, the operator makes 3 an input to the second operator controlled input 4 arrangement 110 to direct pilot pressure through the pilot conduit 106 to move the directional control 6 valve 78 towards its first operable position. In the 7 first operable position, the supply conduit 17 is in 8 communication with the rod end 84 through the supply 9 port 90 and second outlet port 94, the conduit 110, and across the second vented load check valve 88.

11 The valving element 114 of the fourth vented load 12 check valve 88 moves to an open position in response 13 to the pressurized fluid to permit fluid to flow to 14 the rod end 84.

is The exhaust flow from the head end 82 16 returns to the reservoir 18 through the conduit 98, 17 across the third vented load check valve 86 and 18 through the first outlet port 92 and the exhaust port 19 96 of the directional control valve 78. Since the pilot signal in the pilot conduit 106 is also 21 directed to the third two-position valve 118 moving 22 it to its flow passing position, the pressure chamber 23 112 of the third vented load check valve 86 is open 24 to the reservoir 18 thus permitting the valving element 114 to lift up in a conventional manner to 26 pass flow therethrough.

27 When it is desired to retract the first 28 fluid cylinder 26, or rack the bucket back, the 29 operator makes an input to the first operator controlled input arrangement 54 to direct pressurized 31 pilot fluid into the pilot conduit 48 thus moving the 17 1 first directional control valve 24 towards its first 2 operable position. In the first operable position, 3 the supply conduit 17 is connected to the rod end 4 port 30 of the first fluid cylinder 26 through the supply port 36 and second outlet port 40 of the first 6 directional control valve 24, the conduit 46, and 7 across the second vented load check valve 34. As 8 previously noted, the valving element 59 is urged 9 open by the pressurized fluid being directed to the rod end 30.

11 The exhaust flow from the head end port 28 12 is communicated to the reservoir 18 through the 13 conduit 44, across the first vented load check valve 14 32, and the first outlet port 38 and exhaust port 42 of the first directional control valve 24. As 16 previously noted with respect to the other vented 17 load check valves, the valving element 59 of the 18 first vented load check valve 32 is moved to an open 19 position by the first two-position valve 60 being moved to its flow passing position to vent the 21 pressure chamber 56 thereof. The first two-position 22 valve 60 is moved to its flow passing position in 23 response to the pressurized pilot fluid in the 24 conduit 48 that is being directed to the first directional control valve 24.

26 In order to extend the first fluid cylinder 27 26, or dump the bucket, the operator makes an input 28 to the first operator controlled input arrangement 54 29 to direct pressurized pilot fluid to the pilot conduit 50 thus moving the directional control valve 31 24 towards its second operable position. In the 18 1 second operable position, the supply conduit 17 is 2 connected to the head end port 28 through the supply 3 port 36 and the first outlet port 38 of the 4 directional control valve 24, the conduit 44, and across the first vented load check valve 32.

6 The exhaust flow from the rod end port 30 7 is directed to the second outlet port 40 of the first 8 directional control valve 24 through the conduit 46 9 across the second vented load check valve 34. The valving element 59 of the second vented load check 11 valve 34 is moved to an open position in response to 12 the second two-position valve 62 being moved to it's 13 open position by the pressure in the pilot conduit 14 50. The flow at the second outlet port 40 from the is rod end port 30 is directed across the first 16 directional control valve 24 and combined with the 17 fluid in the supply port 36. Consequently, the 18 pressure of the f luid at both the head end port 28 19 and the rod end port 30 are substantially the same.

The first fluid cylinder 26 extends due to the 21 difference in area between the head end of the fluid 22 cylinder 26 and the rod end thereof. Since the 23 forces needed to dump a bucket is normally not large, 24 the forces created by the area differential is sufficient to extend the cylinder or move the bucket 26 to a dump position.

27 In the event the operator elects to raise 28 the bucket by extending the second fluid cylinder 80 29 and simultaneously dump the load by extending the first fluid cylinder 26, the second fluid cylinder 80 31 will not be substantially slowed or stalled since the 19 1 pump' s flow will not automatically go to the lighter 2 load (dumping of the bucket). This is true because 3 the lightly loaded cylinder (first fluid cylinder 26) 4 is being subjected to substantially the same level of pressure that is being generated by the heavier 6 loaded second fluid cylinder 80. Consequently, each 7 of the first and second cylinders 26,80 will move at 8 the rate established by the operator inputs.

9 The operation of the embodiment of Fig. 2 is substantially the same as that of Fig. 1 when 11 simultaneously extending (lifting) the second fluid 12 cylinder 80 and extending (dumping) the first fluid 13 cylinder 26. One difference is that the flow being 14 exhausted from the pressure chamber 56 of the second is vented load check valve 34 through the second two 16 position valve 62 is connected to the conduit 46 at 17 the connection point 125 and has the one-way check 18 valve disposed therein. The one-way check valve 128 19 functions to block any pressurized fluid in the conduit 46 at the connection point 125 from reverse 21 flowing into the pressure chamber 56 of the second 22 vented load check valve 34.

23 The two-position bypass valve 130 functions 24 to permit free flow around the one-way check valve 128 whenever the second fluid cylinder 80 is not 26 being extended (lifting the load). when the first 27 fluid cylinder is being extended, the exhaust flow 28 from the rod end port 30 acts on the valving element 29 59 of the second vented load check valve 34 to open it letting flow pass therethrough and across the 31 first directional control valve 24 to recombine with 1 the pump flow in supply port 36. Pressurized f luid 2 in the pressure chamber 56 thereof is directed across 3 the two-position valve 62, the two-position bypass 4 valve 130 and to the connection point 125 and across the first directional control valve 24 to the supply 6 port 36.

7 When it is desirable to lift the load at 8 the same time the load is being dumped, regenerative 9 flow with pressure equalization, the two-position bypass valve 130 is moved to the blocking position so 11 that the pressurized fluid in the conduit 46 between 12 the first directional control valve and the second 13 vented load check valve 34 is prohibited from 14 reaching the pressure chamber 56 thereof.

is Consequently, the valving element 59 of the second 16 vented load check valve 34 can open to permit the 17 pressure from the pump 16 to also pressurize the rod 18 end port 30 at the same time it pressurizes the head 19 end port 28. Consequently, with pressure equalization of both ends of the first fluid cylinder 21 (dump) with respect to the pressure at the head end 22 port 82 (lift) of the second fluid cylinder 80, the 23 speed of lifting is not slowed or hampered by the 24 simultaneous dumping of the load.

In many applications, it is desirable to 26 perform an operation called "backdragging". This 27 operation exerts a force on the rod of the cylinder 28 urging it in a direction towards the head end of the 29 cylinder. In the subject arrangement, the first fluid cylinder 26 is used to urge the bucket towards 31 a position (extend the cylinder) to performthe 21 1 backdragging operation. During backdragging with no 2 lift, the pressure in the head end of the first fluid 3 cylinder 26 is high due to the forces being exerted 4 on the rod. If the pressure in the head end becomes too great the first diverter valve 68 opens to 6 relieve the over pressure condition. In the event it 7 is desirable to dump (extend the first fluid 8 cylinder) while backdragging with no lift, the pump 9 pressure is prohibited from reaching the rod end port 30. Consequently, the second diverter valve 136 can 11 open with a lower head end pressure to exhaust the 12 flow from the rod end to the reservoir 18. The pump 13 pressure is blocked from the rod end port 30 since 14 the pump pressure in conduit 46 is permitted to by is pass the one-way check valve 128 through the two 16 position bypass valve 130 across the open two 17 position vent valve 62 and into the pressure chamber 18 56 of the second vented load check valve 34. With 19 the pump pressure in the pressure chamber 56 acting on the larger area of the valving element 59, the 21 same pump pressure acting on the opposed smaller area 22 will not permit the valving element 59 to open.

23 When it is desirable to dump the load while 24 lifting, the two-position bypass valve 130 is moved to its blocking position thus the pump pressure 26 cannot get to the pressure chamber 56. The flow 27 being exhausted from the rod end port 30 acts on the 28 shoulder of the valving element 59 to open it thus 29 permitting the rod end port 30 to achieve the same pressure as the pump pressure.

22 1 In the event that the first fluid cylinder 2 is fully extended during simultaneous lifting and 3 dumping, and the mechanism connected to the first 4 fluid cylinder exerts an undue force on the rod which increases the pressure in the head end, the first 6 diverter valve can open to relieve the over pressure 7 condition. Since the force of the second mechanical 8 biasing mechanism 138 is larger than the force of the 9 first mechanical biasing mechanism 72, the second diverter valve 136 remains closed.

11 This arrangement would also prevent the 12 first fluid cylinder 26 from slightly retracting when 13 moving to the dump position with the first fluid 14 cylinder 26 at or near the fully extended position.

is This slight retraction happens because the volume of 16 fluid in the rod end is significantly less than the 17 volume in the head end and when the first directional 18 control valve 24 is shifted into its dump (extend) 19 mode, without the use of the bypass valve 130, both the head and rod ends are open to the pump pressure.

21 Due to the very low volume of f luid in the rod end, 22 the pressure therein increases more rapidly and 23 results in a slight retraction until the pressure in 24 the head end equalizes therewith. Since the bypass valve 130 is in its open position, the pump pressure 26 is allowed to flow thereacross and into the pressure 27 chamber 56 of the second vented load check valve 34 28 thus holding the valving element 59 closed so that 29 the pump pressure cannot get to the rod end port 30 thereof. The pressure in the head end port 28 31 quickly increases which results in a rapid increase 23 1 in the pressure at the rod end port 30. Since the 2 exhaust flow from the rod end port 30 is blocked by 3 the valving element 59 of the second vented load 4 check valve, the pressure increases to a level greater than the pressure in the head end port 28.

6 Once the pressure in the rod end port 30 is larger 7 than the pressure in the pump 16/head end port 28, 8 the valving element 59 will open to allow the flow to 9 exit thereacross.

The operation of Fig. 3 is the same with 11 respect to the operation of the one-way check valve 12 128 and the bypass valve 130. In the embodiment of 13 Fig. 3, the four-way diverter valve 68 functions in a 14 similar manner to the first and second diverter is valves 68,136 of Fig. 2. During a dump operation 16 while backdragging with no lift, the four-way 17 diverter valve 68 is used to drain the rod end to the 18 reservoir 18. Since backdragging induces a force on 19 the rod, the pressure in the head end 28 acts to move the diverter valve 68 to its flow passing position.

21 At the same time the head end pressure is available 22 to the relief valve 70 to limit pressure therein.

23 Like the arrangement set forth in Fig. 2, this 24 arrangement would also function in the same manner to prevent the first fluid cylinder 26 from slightly 26 retracting when moving to the dump position with the 27 first fluid cylinder 26 at or near the fully extended 28 position.

29 Additionally, when lifting with the first fluid cylinder 26 at its fully extended position and 31 fluid from the pump 16 is being exhausted across the 24 1 diverter valve 68 and the relief valve 70, the 2 exhausted fluid is permitted to pass across the two 3 position blocker valve 150 back through the four-way 4 diverter valve 68 to fill the rod end of the first fluid cylinder.

6 The operation of Fig. 4 is basically the 7 same as the operation of Fig. 2 with respect to the 8 one-way check valve 128. However, the bypass valve 9 130 is not needed in this embodiment to dump while backdragging but it would still be needed if there is 11 a desire to prevent the slight retraction of the 12 fluid cylinder 26 before dumping with the fluid 13 cylinder 26 at or near the fully extended position as 14 set forth with respect to Figs 1 & 2 above. The five-way diverter valve 68 functions similar to that 16 of Fig. 2. when dumping (extending the first fluid 17 cylinder), the system operates in the same manner as 18 that of Fig. 2. When backdragging with no lift, the 19 head end port 28 is in communication with the relief valve 70 through the five-way diverter valve 68 and 21 the rod end flow is directed to across the five-way 22 diverter valve 68 and the twoposition blocker valve 23 150 to the reservoir 18.

24 When dumping the load with the first fluid cylinder 26 and lifting the load with the second 26 fluid cylinder 80, the exhaust flow from the rod end 27 port 30 of the first fluid cylinder 26 to the 28 reservoir across the five-way diverter valve 68 is 29 blocked by the two-way blocker valve 150. Since the one way check valve 128 blocks the pump pressure from 31 the pressure chamber 56 of the second vented load 1 check valve 34, the pressure of the fluid in the rod 2 end port 30 increases and in combination with the 3 force of the mechanical biasing mechanism 72 urges 4 the five-way diverter valve 68 back to its spring biased position. The increased pressure in the rod 6 end port 30 acts on the shoulder of the valving 7 element 59 to open it and let the flow exhaust 8 thereacross while maintaining equal pressure on both 9 sides of the first fluid cylinder 26.

In view of the foregoing, it is readily 11 apparent that the subject fluid system 10 is a simple 12 and reliable arrangement that ensures that two 13 different circuits 12,14 may be operated in parallel 14 without one or the other of the fluid cylinders 26,28 is substantially slowing or stalling. This remains true 16 even if the one of the cylinders is lightly loaded.

17 The subject invention further permits one of the 18 circuits to be used to perform a "backdragging" 19 operation while still permitting pressure equalization between the circuits.

21 other aspects, objects and advantages of the 22 invention can be obtained from a study of the 23 drawings, the disclosure and the appended claims.

26 Claims 2 3 1 A fluid system having a single source of 4 pressurized supply fluid that receives fluid from a reservoir and being operable to control multiple loads, 6 the fluid system comprising:

7 a first fluid circuit connected to the single 8 source of pressurized supply fluid and having a first 9 directional control valve connected to a first fluid cylinder having head end and rod end ports, the first 11 directional control valve having a supply inlet port 12 connected to the single source of pressurized fluid, 13 first and second outlet ports connected to the respective 14 head end and rod end ports of the fluid cylinder, and an exhaust port connected to the reservoir; the first 16 directional control valve being movable between a center 17 position and first and second operable positions; in the 18 center position, the supply port, the first and second 19 outlet ports and the exhaust port are blocked from one another; in the first operable position, the supply port 21 is in communication with the second outlet port and the 22 first outlet port is in communication with the exhaust 23 port; and in the second operable position the supply port 24 is in communication with the first outlet port and the second outlet port is in communication with the supply 26 port; and 27 a second fluid circuit connected to the single 28 source of pressurized supply fluid in parallel with the 29 first fluid circuit and having a second directional control valve connected to a second fluid cylinder having 31 head end and rod end ports, the second directional 32 control valve having a supply inlet port connected to the 33 single source of pressurized fluid, first and second 27 1 outlet ports connected to respective head end and rod end 2 ports of the second fluid cylinder, and an exhaust port 3 connected to the reservoir; the directional control valve 4 being movable between a center position and first and second operable positions; in the center position the 6 supply port is blocked from the first and second outlet 7 ports and the head end and rod end ports are blocked f rom 8 the exhaust port; in the f irst operable position the 9 supply port is in communication with the second outlet port and the first outlet port is in communication with 11 the exhaust port; and in the second operable position the 12 supply port is in communication with the f irst outlet 13 port and the second outlet port is in communication with 14 the exhaust port.

is 16 2. The fluid system of claim 1 including a 17 diverter valve operatively connected between the head end 18 of the first fluid cylinder and the reservoir, the 19 diverter valve being biased to a flow blocking position by a mechanical biasing mechanism and the pressure in the 21 rod end of the first fluid cylinder and movable towards a 22 flow passing position in response to pressurized fluid in 23 the head end of the first fluid cylinder.

24 3. The fluid system of claim 2, including a 26 relief valve disposed between the diverter valve and the 27 reservoir.

28 29 4. The f luid system of any of claims 1 to 3 including a f irst vented load check valve disposed 31 between the first outlet port of the f irst directional 32 control valve and the head end of the f irst f luid 33 cylinder and a second vented load check valve disposed 28 between the second outlet port of the first directional control valve and the rod end of the first fluid cylinder.

4 5. The fluid system of claim 4 including a 6 pilot control system having a source of pressurized pilot 7 fluid and a control input arrangement connected to the 8 source of pressurized pilot fluid, the first and second 9 directional control valves being movable from their respective center positions in response to receipt of 11 pressurized pilot fluid being directed thereto from the 12 control input arrangement through respective first, 13 second, third and fourth pilot conduits.

14 6. The fluid system of claim 5 wherein the 16 first and second vented load check valves each have 17 pressure chambers that are in communication with the 18 respective head and rod ends through orificed conduits 19 and the pilot control system includes respective first and second two-position valves spring biased to a closed 21 position and each disposed between the respective 22 pressure chambers and the reservoir, the first two 23 position valve being movable to a flow passing position 24 in response to pressurized pilot fluid being directed to one end of the first directional control valve, and the 26 second two-position valve being movable to its flow 27 passing position in response to pressurized pilot fluid 28 being directed to the other end of the first directional 29 control valve.

31 7. The f luid system of any of claims 4 to 6 32 including a third vented load check valve disposed 33 between the first outlet port of the second directional 29 1 control valve and the head end of the second f luid 2 cylinder and a fourth vented load check valve disposed 3 between the second outlet port of the second directional 4 control and the rod end of the second fluid cylinder.

6 8. The fluid system of claim 7 wherein the 7 third and fourth vented load check valves each have 8 pressure chambers that are in communication with the 9 respective head and rod ends through orificed conduits and the pilot control system includes respective third 11 and fourth two-position valves spring biased to a closed 12 position and each disposed between the respective 13 pressure chambers and the reservoir, the third two 14 position valve being movable to a flow passing position in response to pressurized pilot fluid being directed to 16 one end of the second directional control valve, and the 17 fourth two-position valve being movable to its flow 18 passing position in response to pressurized pilot fluid 19 being directed to the other end of the second directional control valve.

21 22 9. The fluid system of claim 6 wherein the 23 flow from the pressure chamber of the second vented load 24 check valve through the second two-position valve is directed to the reservoir through a connection between 26 the second vented load check valve and the first 27 directional control valve and the fluid system also 28 includes a one way check valve disposed between the 29 connection and the second two-position valve, the one-way 30 check valve permits flow from the two-position towards 31 the connection and prohibits reverse flow. 32 1 10. The fluid system of claim 9 including a 2 two position bypass valve disposed in parallel with the 3 one-way check valve between the second two-position valve 4 and the connection between the second vented load check 5 valve and the first directional control valve, the two 6 position bypass valve being biased towards a flow passing 7 position and movable to a flow blocking position in 8 response to a pilot signal being directed to the second 9 directional control valve through the fourth pilot 10 conduit. 11 12 11. The fluid system of claim 9 or 10 13 including a diverter valve operatively connected between 14 the head end of the first fluid cylinder and the 15 reservoir and a relief valve disposed between the 16 diverter valve and the reservoir, the diverter valve 17 being biased to a flow blocking position by a mechanical 18 biasing mechanism and the pressure in the rod end of the 19 first fluid cylinder and movable towards a flow passing 20 position in response to pressurized fluid in the head end 21 of the fluid cylinder. 22 23 12. The f luid system of claim 11 including a 24 second diverter valve operatively connected between the 25 rod end of the first fluid cylinder and the reservoir, 26 the second diverter valve being biased to a f low blocking 27 position by a second mechanical biasing mechanism having 28 a biasing force greater than the mechanism biasing force 29 of the first diverter valve 30 and the pressure in the rod end of the f irst fluid 31 cylinder and movable towards a flow passing position in 32 response to pressurized fluid in the head end of the 33 first fluid cylinder.

31 1 2 13. The fluid system of any of claims 1 to 10 3 including a diverter valve operatively connected between 4 the head end and the rod end respectively of the first fluid cylinder and the reservoir through respective 6 diverter valve head end and rod end exhaust ports, the 7 diverter valve is movable between a flow blocking at 8 which the respective head end and rod ends are blocked 9 from the respective head end and rod end exhaust ports and a flow passing position at which the respective rod 11 and head ends are open to the respective head end and rod 12 end exhaust ports, the diverter valve being biased to a 13 flow blocking position in response to a mechanical 14 biasing mechanism and the pressure in the rod end of the first fluid cylinder and movable to a flow passing 16 position in response to pressurized fluid in the head end 17 of the first fluid cylinder.

18 19 14. The fluid system of claim 13 including a relief valve disposed between the head end exhaust port 21 of the diverter valve and the reservoir and a two 22 position blocker valve disposed between the rod end 23 exhaust port and the reservoir, the two-position blocker 24 valve being spring biased to a flow passing position and movable to a flow blocking position in response to 26 pressurized pilot fluid being directed to the second 27 directional control valve through the fourth pilot 28 conduit.

29 15. The fluid system of any of claims 1 to 10 31 including a diverter valve operatively disposed between 32 the rod end port of the first fluid cylinder and the 33 second vented load check valve and operatively connected 32 1 to the head end port of the first fluid cylinder, the 2 diverter valve is biased to a position to permit fluid 3 flow between the rod end of the first fluid cylinder and 4 the second vented load check valve and block fluid flow f rom the head end port to pass therethrough by a 6 mechanical biasing mechanism and the pressure of the 7 fluid in the rod end of the first fluid cylinder, the 8 diverter valve is movable to a second position at which 9 the flow from the rod end is diverted towards the reservoir and the flow from the head end port is 11 permitted to pass therethrough towards the reservoir, the 12 diverter valve is movable towards the second position in 13 response to the pressurized fluid in the head end of the 14 first fluid cylinder.

16 16. The fluid system of claim 15 including 17 a relief valve disposed between the head end flow from 18 the diverter valve and the reservoir and a two-position 19 blocker valve disposed between the rod end flow from the diverter valve and the reservoir, the two position 21 blocker valve being biased to a flow passing position by 22 a mechanical biasing mechanism and movable to a flow 23 blocking position in response to pressurized pilot fluid 24 being directed to the second directional control valve through the fourth pilot conduit.

26 27 17. A fluid system substantially as 28 hereinbefore described and illustrated in the 29 accompanying drawings.